Certain types of machinery, such as a fluid pressure operable punch press, for example, inherently present risks of injury to the operator who must exercise extreme caution when operating such a machine. A situation, which may be dangerous to the operator, may occur during a contingent power failure, that is, an unexpected loss of operating fluid pressure or a reduction thereof to a degree insufficient for keeping the punch press operating. Unless some safety means is provided for preventing automatic resumption of operation of the punch press, a restoration of operating fluid pressure may cause the press to restart at such time that the operator may have his hands or other parts of his body in a position to be injured by such untimely restarting of the press.